1. Field of the Invention
The present invention relates to a rolling/sliding part used for example as a cam follower, or as a raceway ring or rolling element in a rolling bearing.
2. Description of the Prior Art
A rolling/sliding part is placed in rolling and/or sliding contact with a mating part during use, as with a cam follower, or a raceway or rolling element of a rolling bearing.
There are several known inventions related to improving the surface condition of the rolling/sliding part to enhance the durability of the surface (raceway surface or rolling surface).
For example, Publication of Examined JP Patent Application No. H1-30008 discloses a bearing rolling element having a surface layer in which a residual stress of over 50 kgf/mm.sup.2 is created, and a rolling surface with scratches formed on it and extending in random directions so as to have a maximum roughness (Rmax) of 0.3-1.5 microns.
Furthermore, Publication of Unexamined JP Patent Application Nos. H2-130205, H2-168021, H3-117723, H3-117724, H3-117725, and U.S. Pat. No. 4,893,387 disclose inventions wherein a multiplicity of recesses are formed in random directions on the surface of such a rolling/sliding part by a barrelling process, so that the RMS (roughness means square) ratio is controlled, and the surface layer is made higher in hardness than the interior with a compressive residual stress produced in the surface layer.
Moreover, Publication of Unexamined JP Patent Application No. H4-54312 discloses an invention related to a bearing part, wherein a shot peening process is used to produce a compressive residual stress greater than 100 kgf/mm.sup.2 in the surface layer, and greater than 40 kgf/mm.sup.2 in a portion 300 microns (.mu.m) below the surface.
With the rolling/sliding part disclosed in the above inventions, excellent durability can be achieved depending on the conditions of use. However, adequate durability is not always possible when the rolling/sliding part is used under conditions of insufficient lubrication, which is the object of the present invention, such as when the rolling/sliding part is used in rolling or sliding contact with another part.
For example, with the disclosure of JP Examined Patent application No. H1-30008, in which only the surface roughness is specified, the wear condition at the tips of the minute protrusions existing on the surface cannot be improved, and when the lubricating condition is severe (insufficient lubrication) there is the possibility of wear progressing at an early stage. That is to say, when the rolling/sliding part is used under severe lubrication conditions, the tips of the minute protrusions make direct contact with the surface of the mating material without the intervention of a thin film of lubricating oil. As a result, wear advances from the tips and wear of the surface progresses rapidly.
Also with the inventions disclosed in Publications of Unexamined JP Patent Application Nos. H2-130205, H2-168021, H3-117723, H3-1177234, H3-117725, and U.S. Pat. No. 4,893,387, a substantially similar problem exists.